Improved gold and silver extraction from a refractory antimony ore by pretreatment with alkaline sulphide leach

The pretreatment of an antimonial refractory gold and silver ore was investigated using alkaline sulphide leaching. The ore assayed 20 g/t Au and 220 g/t Ag and contained predominantly quartz/clay and barite, and to a lesser extent, sulphides such as pyrite, stibnite, sphalerite, zinkenite (Pb9Sb22S42) and andorite (Sb3PbAgS6). The latter mineral was identified to be the most important sulphide phase for the occurrence of gold and silver. Cyanide leaching of the ore consistently resulted in low extraction of gold (49%) and silver (18%) confirming the refractory nature of the ore. Alkaline sulphide treatment of the ore under suitable conditions was shown to leach out up to 85% Sb, which remarkably improved the extraction of silver from < 18% up to 90% Ag in the subsequent cyanidation step. Gold extraction was also enhanced by 20–30%. These findings suggest that alkaline Na2S leaching can be suitably used as a pretreatment method prior to the conventional cyanidation for the refractory Sb-bearing ores.